Here are some other ideas you can use to increase SharePoint usage:
0) Force the users home page to go to the portal via group policy (you will see why below)
1) If you can get upper management to use it, then the rest of the crowd will be more willing to use it: See if you can convince upper management to use an Announcement list that goes out to everyone's email instead of a direct email employees. Put this announcement on the portal home page. Everyone will see the announcements because of step 0 and once this happens over time, they will grow accustomed to this.
2) On this same home page - talk to the human resources and public affairs people to keep fresh pictures of employees or local org events on this page. Sometimes an employee of the month, or employee spotlight. Highlight people doing good things in your organization and keep the content fresh. Ask managers to highlight the people doing good things and getting recognition among their peers. Change the story every week or so. People will read this because if step 0 and you will have a backlog of stories because everyone wants their people to be on the front page.
3) Get your portal site structure and global navigation to mimic your organizations org chart. The closer you can do this, the more sense your site will make to people and they will start navigating to other areas and checking out content. Keep on top of this every month - users hate to see stale links or an old group name. Don't be afraid to archive content that isn't used anymore and get rid of the old names. Because of step 0, they will likely want to see what is new areas of the organization they care about.
4) Take advantage of the social pieces : presence, My Sites. If they are forced to go there with step 0 - they will see who else is there or was there recently. You can make a nice knowledge base of employee skills with the My Sites. Also with correct clean active directory, you can have your employee org chart display on the my sites pages. Pass the digital camera around and make everyone put their picture up. The helps people put faces with names.
5) There are ways to change desktops to search SharePoint using connectors. The more people search your portal, the more they will find on it and return to it in the future. http://technet.microsoft.com/en-us/library/ff899315.aspx
By forcing them to go to the portal throughout the day (searches, browser home page, notes from management) and keeping the content fresh and relevant, the users will get used to going back and eventually will contribute to the kool aid party.
Hope this helps.